There is so much to discuss about these two. Too much. I`ll try to limit myself to their designs this time.
Montresor and Morella are the most obvious antipodes in the comic, from their characters to the design of the spectres. He is the Son of Belial, she is the Daughter of Raphael. He's a tempting demon, she's a guardian angel. He destroys, she heals. His color is red (danger and rage) and hers is green (safety and tranquility).
But notice how both spectres have many golden elements that reflect their relationship to religion. To the timid Morella, her faith grants a sword, a shield, and wings, but then it comes to fierce Montresor, his faith puts him in chains. Morella is inspired, protected, and empowered by faith, while Monty is enslaved.
It also reminds us how in human form they both have jewelry around their necks, which they wear against logic: Morella doesn't remember where she got the locket from or what its meaning is, and Montresor has long since lost faith. And yet the locket and the cross are their invariable attributes. They wear it out of habit, because they feel it's the right thing to do.
They both have wings, but Morella's are big, beautiful, and golden, while Monty's are stumps with remnants of feathers and golden streaks that look like blood.
Curiously, Morella's wings are not classic angel wings. They are not white feathers, they are golden blades. It's the same story with her halo. We are used that in the media halos just hover over the angels' heads but in Morella`s case it is fixed with a separate wire, like an accessory. Of course this may be a tribute to her valkyrie aesthetic but in that case it would be cooler to give her traditional angel wings with individual golden armor on them rather than making her wings entirely steampunk. And tbh the halo has been haunting me since her first manifesting. Wouldn't it be easier to draw a standard flying ring over her head? Why do the authors insist on displaying a separate ribbon to the halo, going down somewhere?
Notice how their spectres information plates are designed.
These are the golden details of their images, which, as I said above, reflect the impact of religion on their lives: Morella has wings and a halo (a separate wire is drawn in the same way), and Monty has chains. Not a tail and horns, but chains. As if the main idea of his spectre is the captivity of his own role, and not the role as such. Continuing the analogy, wouldn't Morella's wings be counterpart to Montresor's chains? This is part of her spectral armor, her protection. And we know that Monty uses his reputation as a bad guy - his chains, as self-defense (slightly overthinking here though).
What I'm trying to say is that Morella`s wings and halo are just a superficial parody of the angelic ones. But Montresor's wings apparently are quite real, they grow out of his back, or at least what's left of them. Their roles of angel and demon were imposed on them. She was given wings, while his wings were cut off. They are an ascended girl and a fallen angel, trapped in their roles as messiah and scapegoat respectively.
Why do you keep a sword if you don't have the strength to use it? Why do you keep the remains of your wings if you can't fly with them?